Wikipedia:Reference desk/Archives/Science/2011 June 5

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June 5

Foods S.PROVEN to include Somatotropin?

can somebody list some?,

Thanks?. — Preceding unsigned comment added by 109.67.42.106 (talk) 02:57, 5 June 2011 (UTC)

This is addressed in Growth hormone, which says that most of the supplements actually advertise that somehow they "release" HGH. The only food I can think of that is sure to contain somatotropin is pituitary... but note that even primate GH is inactive in humans. So if you want GH that is active in humans you have to cannibalize human pituitaries Dawn of the Dead style. No, wait, that doesn't work, because the stuff has to be injected to avoid being broken down by the digestive system. In general - human proteins do many fascinating things, but they are not readily accessible as herbal medicine. Wnt (talk) 06:21, 5 June 2011 (UTC)

Please help me identify unknown bacteria

I initially thought I had Serratia fonticola, but my instructor basically hinted that this is wrong since we didn't see this baterium during lab. I'm thinking I should have a very common bacterium (perhaps an enterobacter). Also, because our reagents are getting old, my Indole red test may be negative or positive; I don't know.

Here's my results: Gram negative rod. Methyl Red: POS. Vogues-Proskauer: NEG. hydrogen sulfide production: NEG. Motility: POS. Citrate: POS. O/F glucose: positive (turned yellow). O/F glucose + 1/2" oil on surface: positive (turned yellow). facultive respiration. Oxidase: NEG. Catalase: POS. Nitrate reduction: POS. Nitrite to Ammonia: POS. Urea hydrolysis: NEG. Casein protien hydrolysis: NEG. Starch hydrolysis (amalase production): NEG. Tryptophan degradation (using tryptone broth): NEG. Phenylalanine deamination: NEG.

All of the following tested positive for acid and gas production: glucose, glycerol, lactose, sucrose, mannitol, maltose. Thank you for the help161.165.196.84 (talk) 04:20, 5 June 2011 (UTC)

There's a policy here about doing homework problems - just out and out giving you the answer is frowned upon. More to the point, I don't know what to do with this information anyway. So to start with let's see if we can figure out the logic to this problem.

• The IMViC test series is meant to identify coliform bacteria. The initials stand for:

• Indole test "Indole red may be positive or negative, I don't know"
• Methyl Red test "Methyl Red: POS"
• Voges–Proskauer test "Vogues-Proskauer: NEG."
• Citrate test "Citrate: POS"

Now even at this point I should point out, there are already unwarranted assumptions. By chance I was just reading about Richard Lenski's famous ten-year E. coli selection experiment, in which he found that in one flask, the bacteria suddenly started to use citrate as a food source. Before long they became quite competent at it, even "speciating" into a large Cit+ population and a small specialist population that could only use glucose. But according to the tests above, Cit+ means your bacterium is not E. coli! Since surprises like this also exist in nature, it's hard to be confident about such tests ... and yet, generations of microbiologists have somehow managed to do extraordinarily good work with them. It boggles the mind. Wnt (talk) 06:10, 5 June 2011 (UTC)

Thank you for the response. To clarify, I do understand Wikipedia's hw policy; I just need some direction. My lab manual says I should look at Citrobacter, but this guy produces hydrogen sulfide (so that's not it). I've gone through the Bergie's manual a few times now, to no avail. I'm thinking I have an enterobacter, but I need help figuring out which one. I KNOW I don't have Bacillis subtillis, Providencia, Morganella, Proteus, Serratia, and probably not Klebsiella or Shigella — Preceding unsigned comment added by 161.165.196.84 (talk) 06:23, 5 June 2011 (UTC)

I don't think it really boggles the mind that much. The fact that such things can and do exist in nature doesn't meant they are common. It's obvious that Cit+ E. coli are rare enough in nature (which was after all one of the reasons the discovery was significant), that the test works the vast majority of the time. The reason the trait is so rare would likely be because in most environments E. coli live in (particularly those likely to lead to E. coli ending up in food or water) the trait isn't beneficial enough compared to the cost. That's hardly surprising or difficult to understand, except perhaps to the founder of conservapedia. Nil Einne (talk) 06:52, 5 June 2011 (UTC)

Well, Citrobacter does not necessarily produce H₂S ... here's an article about 25 strains which don't.^[1] In a pinch, it's a case you could argue. Wnt (talk) 04:50, 6 June 2011 (UTC)

On the other hand, nitrate reduction:POS would seem to me to indicate this is among denitrifying bacteria, and nitrate to ammonia:POS I think means that ccNIR nitrate reductase must be present, though I didn't research alternatives. I don't see anything about ccNIR in Citrobacter. Wnt (talk) 05:00, 6 June 2011 (UTC)

Half-life of Proton-AntiNeutron bound state

The class of exotic atoms consisting of Protons, Electrons, and anti-neutrons would seem potentially interesting, given they might provide a way to store anti-neutrons in a normal matter world. But only if the half-life is long enough. I presume that the anti-neutrons wouldn't get close enough to neutrons in surrounding matter to annihilate. Is that correct? How long would bound proton-antineutron nuclei last?

BTW, what are these sort of atoms called? I can see no reference to them in Wikipedia.88.104.247.65 (talk) 10:08, 5 June 2011 (UTC)

Do you have a reason to think such a combination would be bound? (I'm no QCD expert myself, so if it's blindingly obvious, no big.) --Trovatore (talk) 10:28, 5 June 2011 (UTC)

I don't know about any kind of bound state either, but I would expect that the proton's down quark and one of the anti-neutron's down anti-quarks as well as one of the proton's annihilate quickly, leaving a meson made up of an up quark and a down anti-quark (e.g. a pion or a rho meson). Icek (talk) 13:37, 5 June 2011 (UTC)

That's correct. The proton and the anti-neutron would annihilate each other into a set of mesons almost instantaneously. Dauto (talk) 14:42, 5 June 2011 (UTC)

A neutral pion isn't dissimilar, in that it contains a quark and the corresponding anti-quark, and is stable enough to exist as a known particle. The mean lifetime is only about 10^-16s, which you may consider "almost instantaneous", but it's still far from zero. I know very little about the subject, but it seems plausible to me that a proton-antineutron particle could have a comparable lifetime (which is, of course, far too short for the purpose proposed by the OP). --Tango (talk) 16:45, 5 June 2011 (UTC)

The neutral pion decay is governed by the electromagnetic interaction while the proton-neutron decay is governed by the strong interaction. That makes the latter decay much faster than the former. My back of envelop guesstimate gives about 10^-23s which is pretty much instantaneous by any standard. Dauto (talk) 17:55, 5 June 2011 (UTC)

I guess the thrust of the question was the extent to which the quarks and anti-quark could "see" each-other and annihilate rather than being constrained inside the proton/anti-neutron. If a quark-antiquark pair itself has a measurable half-life, I think that's quite encouraging that a proton/anti-neutron might have have a longer one, though maybe a second is pushing it! Dauto, can you share the back of your envelope?--88.104.247.65 (talk) 20:33, 7 June 2011 (UTC)

Hmmm, how about a He-4 nucleus, an electron, and an antiproton? The presence of the electron means this em 'atom' can never have spin 0, so the nucleus and antiproton are always spinning around each other at some rate and never touch, right...? (somehow I don't think this works that way, but I had to ask) B) Wnt (talk) 05:05, 6 June 2011 (UTC)

No, not right. The anti-proton will be in a s shell state around the nucleus and will have a non-vanishing probability to be found at the origin where it will annihilate one of the nucleons in short time. Dauto (talk) 05:59, 6 June 2011 (UTC)

In your usual atom, electrons don't fall into the nucleus because they're small and bouncy and won't stay put. An antiproton is much heavier, so it's pulled to the nucleus much more easily, and there I guess it's annihilated with a proton or neutron. – b_jonas 09:20, 6 June 2011 (UTC)

EHEC, and now it's biogas

Newest reports now blame biogas. Experts think it is possible that bacteria could mix in the tanks and thus generate new strains. Biogas lobby instantly denies and states that the substrate would be heated for at least one hour to 70C. Now I wonder if that heating takes place at the begining of the process, at the end or two times. I wonder further if that heating would not consume a lot of energy and void the benefits of biogas. Does anyone know some facts and details about that? 77.3.180.185 (talk) 11:16, 5 June 2011 (UTC)

I take it you are talking about the 2011 E. coli O104:H4 outbreak? I cannot find any reports connecting this with biogas - could you provide a link? 81.98.38.48 (talk) 11:44, 5 June 2011 (UTC)

So it probably only available in German language. AFP via Google and the press release from the biogas lobby 77.3.180.185 (talk) 13:10, 5 June 2011 (UTC)

The story you provide only appears to quote one person going by a machine translation. It's also not clear how much expertise they have in the matter (they work for a medical laboratory although in what role is unclear, even what the medical laboratory does is unclear). There's something on the Agricultural and Veterinary Academy which I'm not clear about but I think it's either saying it's unlikely or it's something to look in to (which they probably say with all possible leads) Nil Einne (talk) 15:46, 5 June 2011 (UTC)

The medical laboratory is doing those kinds of test as they are proposing. So if they are right, they would have dug up a really big business for themselves and other laboratories like theirs. Also, they, as well as those from the veterinary academy are not saying the actual EHEC strain does provably come from a biogas facility, only that it was possible that it did. Anyway, my question is about the heating of the substrate for biogas generation and its costs in terms of energy. 77.3.180.185 (talk) 16:19, 5 June 2011 (UTC)

Would seem to be a very big COI then (it's questionable if they even have to be right or just spread enough FUD to get business). And this still doesn't show whether or not they are likely to be experts on the evolution & spread of new E.coli strains who have any idea what they are talking about (your first statement was 'Experts think it is possible') I wouldn't normally expect those who are primarily involved in the testing side of things to be. (As I said about the Agricultural and Veterinary Academy, I can't really understand that part but it sounds to me like they are mostly just saying 'it may be possible, we will look in to it' which from a political POV is better than saying 'the idea is nonsense and the people suggesting it have no idea what they are talking about' even if they really think that.) Also, many things are possible, it doesn't mean it's likely. Nil Einne (talk) 03:16, 6 June 2011 (UTC)

Ha, so Germany may have more deaths due to an industrial accident involving green technology than with nuclear technology. And I think they are also against irradiation of food. :) . Count Iblis (talk) 14:52, 5 June 2011 (UTC)

Whatever you think of German "ecological" politics, believe me, it's worse. 77.3.180.185 (talk) 16:25, 5 June 2011 (UTC)

That hypothesis is newly a week old. It is more likely a fault with the water recycling treatment plant used in bean sprouting. [2]--Aspro (talk) 16:53, 5 June 2011 (UTC)

Since no one else has answered. About the second question, this is not something I have much experience with but while the heating process obviously won't help the equation in favour of biogas I don't see any reason to think it's going to make it completely untenable. Any energy extraction and production system has lots of costs that would be nice to do away to improve the energy efficiency equation with but are ultimately part of the cost. This would include biogas and I doubt the heating cycle is the biggest cost. Since from the sound of it this isn't a new requirement, if biogas is worth it then this would presumably be with the heating cycle requirements. Nil Einne (talk) 03:25, 6 June 2011 (UTC)

About the first question, a simple search for 'biogas heating 70' finds plenty of discussions. [3] for example suggests pre and after heating is done in some circumstances (and also looks at the effictiveness of the sanitisation). [4] shows the heating cycle and suggest it is primarily part of the production/fermentation cycle rather than simply intentional heating for sanitisation purposes. [5] appears to also have two 70 °C preheating cycles although there's little discussion of the biogas production so it's not clear if 70°C is reached there. [6] appears to use a post-heating pasteurisation but doesn't mention much of the initial process. [7] uses a CHP system to achieve 70-90°C apparently to increase production efficiency. [8]and [9] appears to only use pre-heating. From these, I think it's clear it depends a lot on the precise process. Generally pre-heating is the norm, which makes sense from a biological/sanitisation POV. (Remember other outputs would often be fertiliser or compost.) Post-heating may also be done. And in some cases the heating may be part of the fermination process. Nil Einne (talk) 04:08, 6 June 2011 (UTC)

It sounds like one person spouting off with no evidence (except, perhaps, a check from Chevron in his pocket). Yes, biogas uses cow manure or other yucky stuff that could contain E. coli. And 70 C is not really that impressive a method of sterilization, especially when we consider how often accidents happen in waste disposal. (Just work downwind of a city incinerator late at night. It's amazing how many "accidents" happen...) But it could probably much more easily be somebody trying to fertilize the vegetables directly with cow manure or some improperly processed derivative. Or a cow that got loose and wandered into the field. Or... well, just about anything. The investigators have a long, thankless job ahead of them. Wnt (talk) 05:18, 6 June 2011 (UTC)

What is the name of alkane that has 1000 and 10000 carbon atoms?

--Inspector (talk) 14:01, 5 June 2011 (UTC)

1000 is kiliane, but the table of length prefixes for generic long-chain molecules in the IUPAC_Blue_Book does not have 10000. DMacks (talk) 15:45, 5 June 2011 (UTC)

As DMacks mentions, there doesn't appear to be an official term for a 10,000 carbon atom alkane, but note that the factor of tens are based around the SI prefixes. There isn't currently an SI prefix for 10000, but at one time there was myria-, so were there ever a need to have a name for a 10,000 carbon atom alkane, something like "myriane" might be proposed (possibly with "diriane", "tririane", ... for 20000, 30000, etc.). Note that you'll only need those terms if it's a linear alkane of 10,000 carbon atoms. A branched hydrocarbon would be something like "260,375,1503,2673,2654,4536,4675,5430,7650,7895-decahectylnonaliane". As final note, at that size you're really not in the standard hydrocarbon regime, but rather in the land of polymers. Most chemists would likely view a saturated 10000 carbon atom molecule (linear or branched) not as an alkane, but as a polyethylene molecule. - 174.31.219.218 (talk) 17:50, 5 June 2011 (UTC)

Its also kinda moot; the ability to do reasonable organic (non-biological) synthesis on molecules is so small that most organic chemists don't deal with discrete pure substances composed of identical 10,000 carbon-atom chains. As noted by 174.31, very long carbon chains generally fall in the realm of polymer chemistry and polymers are composed of a range of molecular sizes, one sample of polyethylene may have an average chain length of, say, 10,000 monomer units, +/- 1000 units with a certain level of branching, while a different sample may feature a chain length of 20,000 +/- 500 units with less branching, or something like that. You just don't deal with bulk substances composed of pure 10,000 carbon strait-chain hyrdrocarbons. The only other molecules that get that large are biomolecules like nucleic acids and proteins and stuff like that, and that sort of stuff is dealt with by biochemistry, and biochemical molecules do not follow the IUPAC naming standard for obvious reasons. What would be the IUPAC-standard name for hemoglobin? Does it matter? --Jayron32 18:57, 5 June 2011 (UTC)

Hair colour

I was wondering why natural human hair colour has such a narrow spectrum - no greens or blues, no proper red (whatever we may call it). And then I wondered if any of our close relative primates have hair/fur outside of these boundaries? Cheers --Dweller (talk) 18:58, 5 June 2011 (UTC)

There are only a three pigments availible for human hair color. The relative amounts of each determines your hair color. There is brown eumelanin, black eumelanin and pheomelanin, which is redish in color. Whether you have blond, brown, brunette, mousy brown, black, strawberry blond, gray, red, auburn, carrot orange, etc. is determined by how these three pigments are combined in your hair. There is a discussion of this at Human_hair_color#Genetics_and_biochemistry_of_hair_color and in links from there. --Jayron32 19:19, 5 June 2011 (UTC)

Sorry I wasn't clear in my question... I wasn't asking what the mechanism was for producing those colours, I was asking why we evolved with such a narrow spread... --Dweller (talk) 19:30, 5 June 2011 (UTC)

All three pigments are different types of melanin. They are very similar and the genes for them vary by only very small changes. Evolving completely new pigments would require much bigger genetic changes, which makes it much less likely to happen. --Tango (talk) 19:36, 5 June 2011 (UTC)

The technicolor specimens of hominidae got picked off by even the legally blind hawks. DRosenbach ^{(Talk | Contribs)} 19:49, 5 June 2011 (UTC)

What's more remarkable is that this same limited palette is used by so many other mammals - see equine coat color, for example. Even Russian Blue cats are actually just using diffuse black pigment, though looking at one I'd think there must be a bit of structural iridescence at work. Other animals like birds and butterflies have carotenoids and flavonoids; one group of birds invented turacoverdin from scratch. But I just can't think of a mammal right now that goes beyond the black-brown-orange-yellow range of melanins in hair. But I'm probably forgetting something obvious. Wnt (talk) 05:32, 6 June 2011 (UTC)

Mandrills are colorful according to our article, though I have no idea about the pigments they use. – b_jonas 09:13, 6 June 2011 (UTC)

A mandrill's skin is indeed colorful, with blues, reds, pinks, and purpes, but its pelage is dark grey. -- 110.49.251.120 (talk) 15:19, 6 June 2011 (UTC)

Blue in mandrills (and in the vervet monkey's magnificent nutsack) is structural. --Sean 17:01, 6 June 2011 (UTC)

Nice explanation about mandrills' color, both of you. Thank you. – b_jonas 18:28, 6 June 2011 (UTC)

I was going to research this Illyrian poodle^[10] a bit further, but stumbled quickly onto a fairly convincing-looking literature review in, of all places, a cycling forum: [11] which quotes from (in case that link disappears) "P. Sumner and J.D. Mollon Colors of Primate Pelage and Skin: Objective Assessment of Conspicuousness - American Journal of Primatology 59:67-91 (2003) http://vision.psychol.cam.ac.uk/jdmollon/papers/sumner_mollon2003.pdf" which in turn cites Nassau 1983 and Slifka et al, 1999. Wnt (talk) 17:47, 7 June 2011 (UTC)

East and west reversed when looking at the Moon?

The article Near side of the Moon says that although while standing on the Moon, east and west are where you'd expect them to be, when looking at the Moon on the sky, they are reversed. I couldn't understand why, and looking at Talk:Near side of the Moon#Orientation of the Moon, I see I'm not the first one to wonder at this. I thought it could be because of a mirror effect - after all, when standing on the Moon, the lunar surface is below your head, but when looking at it on the sky, it's above your head - but then I looked at the "Blue Marble" photograph on the article Earth, which is a genuine photograph of Earth from space, and it showed east on the right and west on the left, just as you'd expect them to be. Could anyone explain why they are supposed to be the other way around on the Moon? JIP | Talk 19:49, 5 June 2011 (UTC)

The article is not very well written, but maybe what it's getting at is that if you think of the Earth and Moon at a time when the Greenwich meridian is pointing directly at the Moon, then the Western edge of the Earth is "opposite" the Eastern edge of the Moon, and vice versa. It's a similar idea to the (supposed) left-right reversal of the image in a mirror. AndrewWTaylor (talk) 20:07, 5 June 2011 (UTC)

(ec)The statement makes no sense. The moon's orientation in the sky depends on where you are standing on the earth, since the earth is round. Dauto (talk) 20:08, 5 June 2011 (UTC)

I think the question is about the idea of east and west on the Moon itself, which is not obviously a well-defined notion as it stands; some convention must be chosen. You could say that the Moon's "north pole" is the pole that's in the same direction from the Moon's center that the Earth's north pole is from its center. Or, you could say that the Moon's north pole is the pole where the Moon, turning under your feet, turns the same direction that the Earth turns under your feet at the Earth's north pole (that is, counterclockwise, if I've done that right in my head). I think the two definitions would give the opposite answer. --Trovatore (talk) 20:12, 5 June 2011 (UTC) No, I take it back, I think they give the same answer. Still, it's a point that needs further clarification. --Trovatore (talk) 20:14, 5 June 2011 (UTC)

I'm assuming the North Pole on the Moon is the pole that points the same way from the Moon's center as the North Pole on Earth points from the Earth's center. I have no experience on being on the Moon, so the only way I can visualise this is imagining looking at another Earth on the sky instead of the Moon. However, I cannot help but imagine that if I am standing on the Earth, facing north, then east is on my right and west is on my left, both on the Earth under my feet and on the Moon up in the sky. Would the Moon look different if I was facing south? "North is up, south is down" is, to the best of my knowledge, an arbitrary decision and not some irrevocable basic law of physics. Surely it's possible to view the Earth from space as upside down from the "Blue Marble" image? JIP | Talk 20:32, 5 June 2011 (UTC)

When you look at a mirror, why is left and right exchanged, but not up and down? (I know the answer, but I hope the question will lead you to think into the right direction.) 77.3.180.185 (talk) 20:19, 5 June 2011 (UTC)

Please don't forget to end-small next time to prevent everything afterwards from being registered as small. DRosenbach ^{(Talk | Contribs)} 20:29, 5 June 2011 (UTC)

When I look at myself in the mirror, what I am seeing is light that is coming towards the same direction as me, but bounces off the mirror, reversing direction. So it's only natural that left and right are reversed. But when I look at the Moon, what I am seeing is light that is coming towards the same direction as the Moon, just as if I were looking at some other object above my head. There is no mirror up in the sky where the Moon would be reflected. JIP | Talk 21:20, 5 June 2011 (UTC)

When I stand in front of my mirror, Glasgow is miles away to my left. The handsome person in the mirror agrees that Glasgow lies in that direction. In other words, lateral inversion is perceived only in my own reference frame, not in the real outer world. Cuddlyable3 (talk) 07:58, 6 June 2011 (UTC)

The North pole of the moon is defined as that pole pointing in the same direction as the Earth's North Pole. If you are in the Northern hemisphere and the word Moon were written across the face of the moon at its equator as you looked at it, and there were a man walking from the emm toward the enn, he would be walking to the east on the moon but appear to be moving toward the west horizon of the Earth. Simple. μηδείς (talk) 20:52, 5 June 2011 (UTC)

I understand what you mean, but I still cannot visualise it when imagining another Earth orbits the Earth instead of the Moon. (The Earth is the only planet where I know intrisincally where "east" and "west" are supposed to be when on the planet's surface, because I have not been on the surface of any other planet.) JIP | Talk 21:04, 5 June 2011 (UTC)

A standard map of the Earth is oriented in the way you would see it from the outside: East is right, west is left (always taking north to be up). With the night sky things are reversed because we're looking at the celestial sphere from the inside. That's why maps of the night sky are drawn such that east is left when north is up; that's also the standard orientation of astronomical images. Now, with the moon you have two options: Either you consider the moon as hanging in the night sky and you define east and west to be the same directions you assign to the sky, i.e. east is left - I think this is referred to as the "astronomical orientation". Alternatively, you consider the moon to be a physical body, like Earth, and you use the same orientation you would for a globe: east is right - that's called the "astronautical" orientation. The latter is the one that is officially in use today (defined by the IAU in 1961 [12]). Observers of the moon actually prefer the terms "preceding" and "following", referring to the daily motion of the moon (the way the moon would move through the field of view of a fixed telescope). --Wrongfilter (talk) 21:40, 5 June 2011 (UTC)

Where does this notion of "east is left" come from? Does the sky somehow have a different coordinate system as the bodies in it? The only possible way I could see all this as making any sense is viewing the visible sky as a thin, transparent plastic band, with "east is that way" and "west is that way" written on it on the outside. When we look at it from the inside, we see those directions the opposite way. But the Moon is not a thin, transparent plastic band. It is a spheroid, and so it surface wraps around it, and would be the right way around on the near side, which is what we see from the Earth. JIP | Talk 19:21, 6 June 2011 (UTC)

What Wrongfilter wrote makes sense to me. It's natural for the celestial sphere's coordinate system to have the opposite handedness from Earth's on a map, since they can be treated as concentric and we look at them from opposite sides. If north is up on both maps, then east will be left on one and right on the other. For the Moon/Sun/Mars/etc. there are multiple conflicting ways of assigning the names "north" and "east", all with some claim to naturalness, and the only solution is to pick one and standardize it. The maps are never mirrored from what we see; this is purely about word choice. -- BenRG (talk) 22:17, 6 June 2011 (UTC)

Does this mean that when north is up, the same direction is right and the same direction is left both under our feet and up in the sky, we're just labelling them "east" and "west" differently? JIP | Talk 19:38, 8 June 2011 (UTC)

Force = mass x ____

Perhaps I'm just understanding this incorrectly, but suppose I have a post submerged into the ground and I run into it with a horizontal beam fitted to a car that is traveling at a constant speed -- won't the speed of the car have an effect on the force applied to the submerged post. My confusion lies in the idea that force is equivalent to mass x acceleration, and in my example, the car is traveling at a constant speed (and is experiencing no acceleration) -- so why isn't it mass x velocity or something like that? DRosenbach ^{(Talk | Contribs)} 20:27, 5 June 2011 (UTC)

The car is slowed (changes velocity) by the impact of the post. That change in velocity times the mass involved gives the force. μηδείς (talk) 20:55, 5 June 2011 (UTC)

But is that the absolute value? How can it be that a car accelerating at that (positive) absolute value provides the same force as one deccelerating at the (negative) absolute value? And that's sort of using the impact (i.e. the "transfer of force," so to speak) to retroactively provide the acceleration. DRosenbach ^{(Talk | Contribs)} 21:07, 5 June 2011 (UTC)

The force provides the acceleration, rather than the acceleration providing the force. So here, the post decelerates the beam, whilst the beam accelerates the post. - Jarry1250 ^{[Weasel? Discuss.]} 21:18, 5 June 2011 (UTC)

Since the OP has the post embedded in the ground, the force of decelerating the beam and car accelerates planet Earth a little. But fear not Earthpeople, the effect merely reverses the acceleration your planet received when the car started. Cuddlyable3 (talk) 07:51, 6 June 2011 (UTC)

Mass x velocity is something called momentum. This is not force. Is that, perhaps, your confusion? The force you hit the post with is dependent on how quickly you change speed. So, if your initial speed was 50 miles per hour, and you drop to 0 miles per hour in 1 second, you would impart the exact same force on the pole as if you were traveling 100 miles per hour and stopped in 2 seconds. In reality, your stopping time would not double as your speed doubles, indeed it will probably only go up a small amount, so lets say that at 50 miles per hour, your stopping time is 1 second, but at 100 miles per hour your stopping time is 1.1 seconds. You clearly impart more force in the second example because your acceleration (deceleration, whetever, same math with a negative sign) is significantly higher, 100/1.1 is a bigger number than 50/1. --Jayron32 00:28, 6 June 2011 (UTC)

WKD colour loss

Hey all. I kept some leftover bottles of WKD Original Vodka for a couple of months. They were originally the typical blue colour [13], but when I got round to drinking them yesterday, they were colourless. Tasted exactly the same, but colourless. What chemical could be responsible for this? What's the story? Regards, - Jarry1250 ^{[Weasel? Discuss.]} 21:24, 5 June 2011 (UTC)

They weren't by any chance exposed to direct sunlight ? This can cause many colors to fade. Another possibility is that the blue coloring came out of suspension or solution. In that case, I'd expect to see some blue residue, perhaps at the bottom of the bottle. StuRat (talk) 01:03, 6 June 2011 (UTC)

I tried to look up the WKD food coloring, but didn't find it easily. You don't suppose that bottle has an ingredients list? I was thinking that using methylene blue might be rather clever as it can reduce liver necrosis, but methylene blue makes for blue urine, but WKD apparently (from the web search) makes for bright yellow urine. Twas a nice idea while it lasted. Wnt (talk) 05:41, 6 June 2011 (UTC)

:) Um, I don't have the box, only the bottles themselves, and they have only a very vague statement about ingredients. Darn. - Jarry1250 ^{[Weasel? Discuss.]} 16:33, 6 June 2011 (UTC)

They were left outside in a box to keep cool, but the ones hemmed in on all sides are no different from the ones in a little more space. There was no residue in any of the 8 bottles. - Jarry1250 ^{[Weasel? Discuss.]} 16:33, 6 June 2011 (UTC)

Well, then, we're down to a chemical reaction, it sounds. Perhaps the dye reacts slowly with some other component to form clear products. StuRat (talk) 22:47, 7 June 2011 (UTC)

Sound-guided missiles

It seems most new military aircraft are "stealth" and harder to target by heat-seeking or radar guided missiles. Has anybody ever developed a missile that flies towards the source of a loud sound? Would this be possible and how could it work?--92.251.222.88 (talk) 21:41, 5 June 2011 (UTC)

This sounds like a good idea, but it has some problems. For one thing, most anti-aircraft missiles fly over the speed of sound. Even when they don't, the sound of the missile flying at hundreds of miles an hour would overwhelm the microphone. Also, new stealth aircraft are also designed to minimize sound as well as radar. And an aircraft could fly at supersonic speeds and the missile would be useless. I think the next anti-stealth weapon will be low-frequency radar. --T H F S W (T · C · E) 22:29, 5 June 2011 (UTC)

Stealth aircraft are only really stealthy when flying over countres that use pre-1970s air defense systems. Modern air defense systems, like the MIM-104 Patriot or the S-400 (SAM) don't have problems shooting down the most advanced stealth aircraft from more than 100 km distance. Count Iblis (talk) 01:23, 6 June 2011 (UTC)

Could you provide a reference for that? I don;t think stealth fighters are designed with 1970s technology being the primary opposition. Googlemeister (talk) 16:47, 6 June 2011 (UTC)

The Lockheed F-117 Nighthawk design was started in 1975 and first flight of a demonstrator was in 1977, so he's probably right. Alansplodge (talk) 12:59, 8 June 2011 (UTC)

Well F-117s are all retired. I was referring to more modern designs, like the F-35 or the F-22 (even though the F-22 is something like 15 years old now). Googlemeister (talk) 21:22, 9 June 2011 (UTC)

Forget aircraft. I want a noise-seeking missile to take out motorcycles and overly-loud cars. --Carnildo (talk) 23:22, 7 June 2011 (UTC)

See Japanese war tuba and acoustic location. I don't know if any torpedoes used ASDIC. 92.24.128.171 (talk) 18:07, 8 June 2011 (UTC)

Safety of BPA-free plastic water bottles

The plastic water bottles sold these days all seem to claim to be BPA-free. However, they all seems to have some "plasticky" smell, suggesting chemical emissions. What material(s) are BPA-free plastic water bottles usually made of? Do we actually know that these materials are safer than the polycarbonate they replace, or are we just trading one known hazard for some other unknown ones? --173.49.79.135 (talk) 23:59, 5 June 2011 (UTC)

It's largely a ruse that water bottles need be free of bisphenol-A because it's so dangerous, because many other things still contain it, such as most of the esthetic white dental fillings (composite, glass ionomer, etc.) Are we looking at a threshold? How much is "too much"? Apparently, it doesn't make too much of a difference. DRosenbach ^{(Talk | Contribs)} 03:39, 6 June 2011 (UTC)

I'd go with your instincts here. If you can smell it and/or taste it, then a significant quantity of chemicals must be given off by the bottle. Whether those chemicals pose a health risk is probably unknown, but it seems reasonable to avoid them, wherever possible, say by using glass bottles. StuRat (talk) 04:02, 6 June 2011 (UTC)